Electro-optical sensor

ABSTRACT

This invention is directed to an electro-optical sensor which can accurately measure small displacements. The sensor utilizes a modulated light source and has a shutter whose displacement controls the light which impinges on a pair of phototransistors. The phototransistors are connected to a transformer and their output is a measure of the displacement of the shutter.

United States Patent 1 1 Brown et al. Nov. 6, 1973 [54] ELECTRO-OPTICALSENSOR 3,502,894 3 1970 Schcrr 250/231 R [75] Inventors: Charles H.Brown, Phoenix, Ariz.;

I Frederic L. Miller, San Diego, Calif. Primary Examiner Richard AFarley [73] Ass1gnee: The United States of America as Attorney-Thomas 0,Watson, Jr.

represented by the Secretary of the Navy 22 F1 (1: A 25 1971 1 57ABSTRACT [21] Appl. No.: 174,918

Related U.S. Application Data Continuation of Ser. No. 786,839, Dec. 19,1968, abandoned.

U.S. Cl. 356/152, 250/220 R Int. Cl. G01b 11/26 Field of Search 356/141,152;

250/219 DR, 220 R, 231 R References Cited UNITED STATES PATENTS 2/1968Kohl 356/152 AC INPUT This invention is directed to an electro-opticalsensor which can accurately measure 7 small displacements. The sensorutilizes a modulated light source and has a shutter whose displacementcontrols the light which impinges on a pair of phototransistors. Thephototransistors are connected to a transformer and their output is ameasure of the displacement of the shutter.

10 Claims, 1 Drawing Figure PATENTEDNDY e 1975 AC INPUT INVENTORS CHAHLE5 H. BROW/V FEEDER/C L MILLER ATTORNEY STATEMENT OF GOVERNMENT INTERESTThe invention defined herein may be manufactured and used by or for theGovernment of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

FIELD OF THE INVENTION 1. Background of the Invention This invention isdirected to an electro-optic sensor. It is utilized to provide accuratemeasurements of small displacements such as those provided by anaccelerometer sensor, a force transducer, a pressure transducer or thelike. i l

2. Description of the Prior Art Sensors utilized in the prior art tomeasure displace ment had two major disadvantage s. In the first placethe reaction force between the sensor and the object whose displacementwas measured introduced inaccuracies into the measurements.

In the second instance the prior art sensors could not be used inredundant systems where fail passive operation is essential.Additionally, the prior art displacement sensors were relatively largeand complex and required very complex accurate construction methods.

SUMMARY OF THE INVENTION The inventive sensor yields highly accurateoutputs and represents a significant advance ovethe prior art. Byconverting light to electricity the sensor exerts a near zero reactionforce on the object whose displacement is to be measured. Thesensorprovides fail passive operation because upon failure its outputfalls to zero or a lower gradient and not to a hard or steady stateoutput and is therefore useful in redundant systems. Furthermore, thesilicon phototransistors utilized provide an amplification of themeasured signal in addition to converting its energy form.

The design of the inventive circuit is very simple and it is easy toconstruct. Furthermore, since the phototransistor may be made byphoto-etching or similar microelectronic techniques, the size of thesensor may be extremely small.

The inventive sensor utilizes a light source activated by alternatingcurrent to energize two phototransistors. A shutter attached to apressure transducer or the like controls the light which impinges on thephototransistors. The collectors of the phototransistors are connectedin a push-pull arrangement to either side of a center tappedtransformer. A direct current supply is connected to the center of thetransformer. The output of the sensor is taken from the secondarywinding of the transformer and is a function of the position of theshutter.

It is an object of this invention to provide an electrooptical sensorwhich yields accurate results.

It is a further object of this invention to provide a fail passiveelectro-optical sensor.

It is a further object of this invention to provide an electro-opticalsensor which exerts a zero reaction force on the transducer to which itis connected.

BRIEF DESCRIPTION OF FIGURES These and other objects, advantages andnovel features of this invention will become apparent from the followingdetailed description and drawing wherein the FIGURE sets forth theinventive circuit.

DESCRIPTION OF PREFERRED EMBODIMENTS The sensor receives an' alternatingcurrent input signal at terminals 11 and 12 and passes it to a galliumarsenide diode 13 where it is converted to light. If desired, anincandescent light could be used in place of the diode.

Optical fibres 14 are used to conduct the light to shutter 15. Shutter15 is connected to a pressure transducer or the like so as to moverelative to the fibre opticas and apertures 18 and 19. Since themovement of the shutter is unimpeded, it exerts little or no reactionforce on the transducer.

The shutter has two slits the first of which 16 is associated withaperture 18 and the second of which 17 is associated with aperture 19 asseen in the drawing. The placement of these openings is such that onlyone opening will pass light from fibre optics 14 to its associatedaperture at any given position of the shutter.

Phototransistors 21 and 22 are mounted adjacent to apertures 18 and 19.The collectors of the phototransistors are connected to a center-tappedtransformer 23 and the emitters are connected to ground throughresistors 26 and 25. Adirect current source is connected to the centertap 24 of transformer 23. The transformer is designed to preventshorting of the primary to the secondary windings.

The phototransistors are very sensitive to light and yield very accurateresults. They may be made by photoetching or similar techniques. Theiraccuracy and size facilitate the simplicity of design apparent in theinventive circuit.

In operation, the input source at 11 and 12 alternately excites thediode 13 which then emits modulated light. This light is conducted toshutter 15 by fibre optic 14.

The displacement of shutter 15 is controlled by the transducer to whichit is connected. When slit 16 is aligned with aperture 18,phototransistor 21 will be energized and when slit 17 is aligned withaperture 19, phototransistor 22 will be energized. The light gives aforward bias to the transistors and their conduction is controlled bythe amount of light received.

When the phototransistors are turned on, the conduction path is from thedirect current source connected at 24 through transformer 23,phototransistor 21 or 22, and resister 26 or 25 to ground.

The photoelectric circuit amplifies the modulated light received at thephototransistors. The amplification is analogous to that achieved whenan electric signal is received at the base of a transistor amplifier.The modulated light from 13 causes the phototransistors to turn on andoff. This on and off operation in turn provides an A. C. pulsed outputat terminals 27 and 28 of transformer 23. The amplitude of the pulseswill be a function of the amount of light received by phototransistors21 and 22 which is in turn a function of the displacement of shutter 16caused by the pressure transducer or the like. The transformer isolatesthe amplified alternating current signal from the direct current sourceto provide -'fail passive operation if any of the phototransistorcircuit components short.

A variety of utilization circuits may be connected to the output of thetransformer. These circuits may presexit a visual display, correlated toprovide an indication of the parameter measured or they may initiate avariety of circuits which are responsive to various levels of theparameters measured.

It is seen then that a new and highly accurate electrooptical sensor hasbeen provided. The sensor exerts little or no reactive force on themember to be measured and its operation is fail passive.

What is claimed is:

1. An electro-optical sensor for sensing the displacement of atransducer comprising:

a light source;

an alternating current supply connected across said light source;

an apertured shutter having first and second apertures for attachment toa transducer to be displaced thereby and operable to control the lightreceived by a photoelectric detector;

a photoelectric detector mounted adjacent to the apertured shutter onone side thereof, said photoelectric detector utilizing two sistors,

one of said phototransistors being mounted adjacent V to said firstaperture in said-shutter and the other phototransistor being mountedadjacent to said second aperture in said shutter,

said photoelectric detector being operable to receive light from saidsource to convert the received light to an electric signal; output meansproviding an electrical output which is proportional to the lightreceived by said detector,

said output means comprising a centertapped transformer connected to thecollectors of said two phototransistors, a direct current sourceconnected to said center tap and a pair of resistors connected betweenthe emitters of said phototransistors and ground; and

a pair of light pipes each having one end mounted adjacent to said lightsource and one end adjacent to said first or second apertures in saidshutter.

2. An electro-optical sensor for sensing the displacement of atransducer as in claim 1 wherein said light source is a gallium arsenidediode.

3. An electro-optical sensor for sensing the displacement of atransducer as in claim 1 wherein said light source is a lamp.

4. A photoelectric sensor comprising;

phototranmeans for sensing mechanical movement and for pro-.

viding a physical response to such movement; means for illuminating saidmovement sensing means with light; means for receiving said light in anamount that varies with the magnitude of the physical response of saidmovement sensing means, said light receiving means comprising onephototransistor;

means for providing an electrical output signal which is proportional tothe amount of light received by said light receiving means and operableto prevent an output signal from being generated in response to ashorting failure of said phototransistor.

5. A photoelectric sensor as in claim 4, wherein the movement sensingmeans comprises a transducer which senses mechanical movement and anapertured shutter which is displaced by said transducer to produce saidphysical response.

6. A photoelectric sensor as in claim 4, wherein:

said light receiving means comprises a plurality of phototransistors;

said movement sensing means comprises a shutter having a plurality ofapertures corresponding to the number of phototransistors; and

said light receiving means and said apertured shutter are arranged sothat one of said phototransistors is mounted adjacent to itscorresponding aperture in said shutter.

7. A photoelectric sensor as in claim 4 wherein said illuminating meansis a modulated light source.

8. A photoelectric sensor as in claim 7 wherein:

said output means comprises a transformer which provides a. anelectrical output signal when said phototransistor is operative andreceives said modulated light; and

b. no electrical output when said phototransistor is opened or shorted,even -though said phototransistor receives said modulated light.

9. A photoelectric sensor as in claim 7 wherein:

said light receiving means comprises a plurality of phototransistors;and

said output comprises a transformer which provides a. an electricaloutput signal from any of said plurality of phototransistors that areoperative and re ceive said modulated light; and

b. no electrical output from any of said plurality of phototransistorsthat are opened or shorted, even though such phototransistor receivessaid modulated light.

10. A photoelectric sensor as in claim 7 wherein:

said light receiving means comprises a second phototransistor;

said output means comprises a direct current source connected to thecenter tap of a transformer;

the collectors of both of said phototransistors are connected to theends of the center tapped transformer and their emitters are connectedto ground through a pair of resistors;

said transformer. prevents the generation of a direct current signal inthe output when either of said phototransistor shorts.

1. An electro-optical sensor for sensing the displacement of atransducer comprising: a lighT source; an alternating current supplyconnected across said light source; an apertured shutter having firstand second apertures for attachment to a transducer to be displacedthereby and operable to control the light received by a photoelectricdetector; a photoelectric detector mounted adjacent to the aperturedshutter on one side thereof, said photoelectric detector utilizing twophototransistors, one of said phototransistors being mounted adjacent tosaid first aperture in said shutter and the other phototransistor beingmounted adjacent to said second aperture in said shutter, saidphotoelectric detector being operable to receive light from said sourceto convert the received light to an electric signal; output meansproviding an electrical output which is proportional to the lightreceived by said detector, said output means comprising a centertappedtransformer connected to the collectors of said two phototransistors, adirect current source connected to said center tap and a pair ofresistors connected between the emitters of said phototransistors andground; and a pair of light pipes each having one end mounted adjacentto said light source and one end adjacent to said first or secondapertures in said shutter.
 2. An electro-optical sensor for sensing thedisplacement of a transducer as in claim 1 wherein said light source isa gallium arsenide diode.
 3. An electro-optical sensor for sensing thedisplacement of a transducer as in claim 1 wherein said light source isa lamp.
 4. A photoelectric sensor comprising: means for sensingmechanical movement and for providing a physical response to suchmovement; means for illuminating said movement sensing means with light;means for receiving said light in an amount that varies with themagnitude of the physical response of said movement sensing means, saidlight receiving means comprising one phototransistor; means forproviding an electrical output signal which is proportional to theamount of light received by said light receiving means and operable toprevent an output signal from being generated in response to a shortingfailure of said phototransistor.
 5. A photoelectric sensor as in claim4, wherein the movement sensing means comprises a transducer whichsenses mechanical movement and an apertured shutter which is displacedby said transducer to produce said physical response.
 6. A photoelectricsensor as in claim 4, wherein: said light receiving means comprises aplurality of phototransistors; said movement sensing means comprises ashutter having a plurality of apertures corresponding to the number ofphototransistors; and said light receiving means and said aperturedshutter are arranged so that one of said phototransistors is mountedadjacent to its corresponding aperture in said shutter.
 7. Aphotoelectric sensor as in claim 4 wherein said illuminating means is amodulated light source.
 8. A photoelectric sensor as in claim 7 wherein:said output means comprises a transformer which provides a. anelectrical output signal when said phototransistor is operative andreceives said modulated light; and b. no electrical output when saidphototransistor is opened or shorted, even though said phototransistorreceives said modulated light.
 9. A photoelectric sensor as in claim 7wherein: said light receiving means comprises a plurality ofphototransistors; and said output comprises a transformer which providesa. an electrical output signal from any of said plurality ofphototransistors that are operative and receive said modulated light;and b. no electrical output from any of said plurality ofphototransistors that are opened or shorted, even though suchphototransistor receives said modulated light.
 10. A photoelectricsensor as in claim 7 wherein: said light receiving means comprises asecond phototransistor; said output means comprises a direct currentsource connecteD to the center tap of a transformer; the collectors ofboth of said phototransistors are connected to the ends of the centertapped transformer and their emitters are connected to ground through apair of resistors; said transformer prevents the generation of a directcurrent signal in the output when either of said phototransistor shorts.